Recently, from the viewpoint of conservation of global environment or improvement in fuel consumption, hybrid cars or electric vehicles have been rapidly developed.
Furthermore, various functions for controlling vehicles have been rapidly electronized. Braking of vehicles is also being shifted from a conventional mechanical hydraulic control to electric hydraulic control, and various electric braking systems are proposed.
When an important function such as braking is out of order because voltage reduces in a battery used as a power supply or certain contingencies occur and power is not supplied, hydraulic control cannot be carried out. Therefore, a redundant system using an emergency power supply is often provided.
Conventionally, a method using another battery as an emergency power supply has been proposed. However, a battery has a characteristic of deteriorating over time and its expected lifetime is at most five years when it is used for a vehicle.
Furthermore, it is difficult to detect deterioration in the process and to exhibit a function as an emergency power supply when certain contingencies occur.
Recently, as an emergency power supply substituting for a battery, much attention has been focused on a capacitor such as an electric double layer capacitor. When a capacitor is used in a way in which, for example, charging is carried out when a system is operating and discharging is carried out when a system is not operating, the lifetime of the capacitor can be extended to several times as the lifetime of a battery. Therefore, it is said that a capacitor can withstand the use for 15 years, that is, a target lifetime of a vehicle.
Furthermore, by monitoring characteristic value of a capacitor such as electrostatic capacity and internal resistance, it is possible to understand the change in the characteristics.
Note here that prior art document information as to such a capacitor unit includes, for example, Japanese Patent Unexamined Publication No. 10-189402.
Furthermore, conventionally, a capacitor, other circuit components and a circuit board have been mounted as follows. FIG. 14 is an example of a sectional view showing a conventional mounting. In FIG. 14, on circuit board 501, circuit components 502 constituting a necessary circuit portion are mounted. In general, circuit board 501 is used with the end portion thereof fixed to attaching portion 505 of case 504 by using screw 503, etc.
Information on such a conventional technology is disclosed in, for example, Japanese Utility Model Unexamined Publication No. S63-97286.